1. Field of the Invention
This invention relates to a method of forming a pattern. More particularly, it relates to a pattern forming method which can reliably form, at a very high accuracy, the patterns of various resists including photoresist, electron-beam resist, etc. (in this specification, such patterns shall be generally termed "resist pattern").
2. Description of the Prior Art
As is well known, a resist pattern is formed in such a way that desired parts of a resist film applied on an object surface on which the pattern is to be formed are selectively irradiated by an ultraviolet light, electron beam, X-ray, etc. (in this specification, these shall be simply termed "light"), whereupon a development is carried out.
When the resist is of the negative type, the solubility of the part irradiated by the light lowers; and when the resist is of the positive type, the solubility increases. Therefore, when the unhardened parts of the resist (parts of higher solubility) are subsequently removed by executing the proper developing treatment, the resist pattern having a desired shape is formed.
In such prior-art method of forming the pattern, however, the developing step has resorted to the wet process employing a suitable developing solution. Therefore, the resist film has been swollen with the developing solution, and it has been difficult to accurately form a microscopic pattern.
It is obvious that, in order to prevent the swelling of the resist film due to the developing solution, a dry type development may be made with any of various dry etchings such as plasma etching and sputter etching without using any developing solution.
However, merely by changing only the developing step from the wet process to the dry process in the prior-art pattern forming method, it has been impossible in practice to selectively remove only the unhardened area of the resist film by the dry etching and to accurately form the microscopic pattern because the difference of etching rates for the hardened area and unhardened area of the resist film is small.